There has been proposed a phase modulating apparatus that uses a phase modulated spatial light modulator to modulate the phase of a laser beam in accordance with a phase pattern calculated by a computer. In the phase modulating apparatus, a phase pattern is written to the phase modulated spatial light modulator to be irradiated by a laser beam, so that phase modulation light modulated with the phase pattern is generated.
Japanese Patent No. 2,785,427 describes a method of modulating the phase and intensity of light by utilizing a TN-liquid-crystal spatial light-modulating element. In this method, a phase pattern to be displayed on the TN-liquid-crystal spatial light modulating element is formed in consideration of the phase distortion that occurs due to the drive voltage applied across the TN liquid-crystal.